The present invention relates to an apparatus for applying coatings. The apparatus is adapted to apply a supply of solidifiable, finely divided vitreous coating material, such as glass, or enamel, to the internal surface of a heated, horizontally rotating, cylindrical article, such as a vessel, or tank to form a smooth, uniform, continuous, fused coating thereon.
Glass lined vessels have found widespread use in numerous industries, particularly those industries which require the storage or reaction of corrosive materials. Such vessels find use in extraction, suspension and distillation processes. The glass lining facilitates the use of the vessels under adverse temperature and corrosive conditions.
Various methods and apparatus have been proposed to apply internal coatings to tubular articles, such as reactors. Typical examples of these are: U.S. Pat. Nos. 3,351,289; 3,484,266; 3,827,633; 3,876,190, and 4,150,176. Generally booms, or lances, consisting of an elongated tubular member are utilized. Coating material is fed in one end, transported through the tube portion, to and through, a distribution means located in the end of the boom positioned within the article being coated. As the boom moves through the length of the article, the interior of the article is coated.
In coating vitreous material, such as glass, on steel, it is imperative that an integral coating be obtained. Small defects, such as areas not coated completely, pinholes, blisters, or abrasions, result in rapid deterioration of the substrate in the defective area, especially when the coated article is subjected to corrosive conditions. Methods of distributing particles into a heated article utilizing a fluid carrier, such as air, are generally not adaptable to use in coating processes using vitreous materials as the fluid flow within the article being coated carries particles to undesired locations, causes detrimental localized cooling and results in a substantial amount of suspended particulate material being lost in the exiting flow.
The most widely used prior art method of applying a vitreous coating to the interior of an article involves the room temperature surface application of particulate vitreous material in a carrier, such as water. After the mixture is applied, the article is dried to remove the carrier and subsequently fired. This process is repeated several times to obtain the desired coating thickness. Most prior art processes, such as U.S. Pat. No. 3,484,266, noted above, initially distribute particulate materials on the vessel surface and subsequently in a separate step fuse the particles to obtain the finished coating. The reason a subsequent, and separate, firing step is required, is that mechanical apparatus, such as mechanisms to feed and distribute particulate glass, do not reliably operate at glass firing temperatures. Typically, such temperatues range between about 1500.degree. and about 1850.degree. F. At such temperatures, the particulate feed material frequently becomes tacky and difficult to feed or distribute. The result frequently is an uneven or otherwise defective coating.
U.S. Pat. No. 3,788,874 teaches a method of glass coating by maintaining the article to be coated at a temperature at least as high as the fusion point of the glass, while depositing glass particles on the article at a rate no greater than the rate at which the particles fuse to the article. While this method has many advantages it has not been widely utilized on a commercial basis because equipment to facilitate the commercial use of the method has not been developed. The present invention provides a particle distributing means by which the method of U.S. Pat. No. 3,788,874 may be carried out. The teachings of U.S. Pat. No. 3,788,874 are incorporated herein by reference.